The Electrical, Mechanical, and Electromagnetic Interference Shielding Properties of Oriented Multilayered Polymer Composites Based on polypropylene/Carbon Black

Soft strain sensors based on conductive polymer composites (CPCs) provide a simple and feasible detection tool in wearable electronics, soft machines, electronic skin, etc. However, the CPCs-based soft strain sensors exhibit resistive viscoelasticity (or time-dependent properties) that hinder the intuitive reflection of the accurate strain and a simple calibration process. In this paper, CPCs with different carbon nanotubes (CNTs) and carbon black (CB) contents were prepared, and electro-mechanical experiments were conducted to study the effect of filler dimensionality and content on the resistive viscoelasticity of CPCs, aimed at guiding the fabrication of CPCs with low resistive viscoelasticity. Furthermore, resistive viscoelasticity and mechanical viscoelasticity were compared to study the origin of the resistive viscoelasticity of CPCs. We found that, at the vicinity of their percolation threshold, the CPCs exhibit high resistive viscoelasticity despite their high sensitivity. In addition, the secondary peaks for CB/SR composite were negligible when the CB concentration was low. Generally, compared with one-dimensional CNT-filled CPCs, the zero-dimensional CB-filled CPCs show higher sensitivity, lower resistive hysteresis, lower resistance relaxation ratio, and better cyclic performance, so they are more suitable for sensor usage. By comparing the resistive viscoelasticity and mechanical viscoelasticity of CPCs, it is indicated that, when the concentration of nanoparticles (NPs) approaches the percolation thresholds, the resistive viscoelasticity is mainly derived from the change of conductive network, while when the concentration of NPs is higher, it is primarily due to the unrecoverable deformations inside the material.

The development of high-performance electromagnetic interference (EMI) shielding materials is of great significance for preventing EM radiation. For traditional shielding materials, the pursuit of superior conductivity is the primary designing strategy to achieve highly efficient shielding performance. However, high conductivity will inevitably produce serious EM wave reflections and cause secondary EM radiation pollution. Therefore, absorption-dominated EMI shielding materials known as “green shielding materials” have become an ideal solution for conferring reliable EMI protection to next-generation electronics in complex EM environments. Conductive polymer composites (CPCs) as novel shielding materials have advantages in terms of flexible processability and adjustable EMI shielding performance, hence providing possibility to obtain absorption-dominated shielding materials. In this review, we introduce the evaluation method of absorption-dominated EMI shielding materials and discuss principles and strategies for designing efficient absorption-dominated shielding polymer composites. The recent advances of structural design approaches and processing methods of green shielding CPCs as well as the shielding mechanism of CPCs with low reflection shielding characteristics are systematically summarised. Major challenges of designing efficient EM wave dissipation structure are discussed and potential research frontiers in developing advanced absorption-dominated EMI shielding polymer composites are prospected. It is expected that green EMI shielding CPCs with high efficiency and long-term durability, favourable environmental adaptability as well as multifunctionality will eventually be widely used in the EM compatibility and protection of the next-generation electronic devices.

Conductive polymer composites fabricated by adding a certain amount of conductive fillers, such as carbon black or carbon nanotube, into a polymer substrate are commonly used as the material of the bipolar plate in fuel cells. The electrical conductivity of polymer composites is affected by the distribution and orientation of fillers and is therefore crucial to be assessed. This study is to develop methods and techniques for nondestructively measuring properties of carbon fibers in the conductive polymer composite using a high frequency ultrasound system. The experiments were carried out from samples, fabricated by an injection molding machine, composed of a 5×5 cm polycarbonate added with carbon fibers of 6 µm diameter and 3 mm length and those of weight percentage at 0, 0.1, 0.2, and 0.3%. The ultrasonic signals of conductive polymer composites associated with different filler concentrations were acquired from a 48 MHz high frequency ultrasound imaging system. The raster scanning images corresponding to depths at 0.15 and 0.3 mm beneath the surface of conductive polymer composites were reconstructed. The orientation of filler carbon fibers parallel or perpendicular to the surface of conductive polymer composites were calculated according to their respective percentages of pixel content in the image. Results showed that percentages of pixel contents for fillers of carbon fibers at the depth of 0.15 mm beneath the surface of sample for those 0.1, 0.2, and 0.3 wt% filler carbon fibers were calculated to be 2.50±1.13, 5.19±1.70, and 5.93±1.29, respectively, and those of 0.3mm were to be 2.91±1.46, 6.18±1.60, and 6.42±1.77, respectively. Moreover, those percentages of pixel contents for fillers of perpendicular orientation with respect to depth of 0.15mm were 1.49±0.89, 2.49±0.96, and 3.62±0.95, respectively; those of 0.3mm were 1.39±0.72, 2.70±0.62, and 3.97±0.94, respectively. This study demonstrated that current high frequency ultrasound image incorporated with the analysis method is feasible to be applied to quantitatively and rapidly assess the distributions of fillers in conductive polymer composites.

Acoustic-assisted 3D printing based on acoustofluidic microparticles patterning for conductive polymer composites fabrication

Conductive polymer composites with segregated structures

Conductive polymer composite (CPC) is a very significant research topic in the area of self-regulating heating. It acts in self-regulated heating mode due to its positive temperature coefficient (PTC) effect. PTC effect is the consequence of breakup of conductive paths formed in CPC due to heat up of polymer composite. Currently a good number of researchers are going on conductive polymer composites. In this paper, the important aspects of conductive polymer composites; such as: conduction process, positive temperature co-efficient effect, negative temperature co-efficient etc has been analyzed. Moreover, a summary of the researches conducted by researchers in the fields of conductive polymer composites by employing hybrid fillers has also been discussed.

Highly conductive thin films with suitable mechanical performances play a significant role in modern electronic industry. Herein, a series of ternary conductive polymer composites were fabricated by incorporating carbon black (CB) into binary conductive polymer composites of poly(amide-imide) (PAI) and polyaniline (PANI) to enhance their mechanical and conductive properties simultaneously. By varying the composition of PAI/PANI/CB ternary films, the conductivity enhanced by two orders of magnitude compared with the sum of PAI/PANI and PAI/CB binary conductive polymer composites, and a high conductivity of 1160 S m−1 was achieved. The improved conductivity is mainly because much more continuous conductive networks were constructed in the ternary conductive polymer composites. With the help of the unusual morphology, the tensile strength was also enhanced by more than 80% from 21 to 38 MPa. The origin for the improved morphology was discussed for further improvement.

Tunable electromagnetic interference shielding performance of polypropylene/carbon black composites via introducing microcellular structure

Titanium aluminium carbide powder was reaction synthesized and used as reinforcement in the aircraft grade epoxy matrix (LY556) to develop a high-performance conductive polymer composite. The particle sizes of 4 and 7 µm were employed from 0 to 40 wt.% to improve the mechanical and electrical properties of conductive polymer composites. It was observed that the percolation characteristics were exhibited at a critical threshold of 20 wt.% for both the filler particle sizes. Further, microstructural observations revealed the formation of a conductive network in the conductive polymer composites when the filler content was 20 wt.%. The tensile and flexural properties were increased when the particle size was decreased. Experimental values were then compared with the available analytical models for validation. The mechanical and electrical properties of the conductive polymer composites were optimized by tailoring the filler particle size to 4 µm and particle loading at 20 wt.%. Compared to neat epoxy, the optimized conductive polymer composites have shown a simultaneous increase in strength, stiffness and conductivity performances, which can find applications in aerospace and electronics industries.

This study explores the synergistic effects of hybrid graphite (GR) fillers combined with carbon fibers (CFs) and carbon black (CB) on the performance of PVDF‐based conductive polymer composites (CPCs). Composites were formulated with a fixed GR loading of 60 wt% using optimized mixtures of GR particle sizes: G1 (5.9 μm), G2 (17.8 μm), and G3 (561 μm). To investigate the synergistic effect of hybrid carbon additives on CPCs performance, up to 10 wt% of GR was replaced with CB, CF, or a CB/CF mixture. The G2/G3 (3:1) system showed optimal binary GR performance, with a decomposition temperature of 425°C, through‐plane/in‐plane resistivities of 0.66/0.58 Ω cm, and flexural/compressive strengths of 41.5/17.1 MPa. Replacing 7.5 wt% of G2/G3 with CF improved thermal stability (440°C) and lowered through‐plane/in‐plane resistivities (0.33/0.17 Ω cm), although it slightly decreased flexural/compressive strengths (37.2/13.0 MPa). Replacing 5 wt% with CB reduced thermal stability (400°C) but further lowered both resistivities (0.23/0.16 Ω cm), along with reducing strengths (19.5/5.2 MPa). A ternary mixture (CF/CB: 2.5/7.5 wt%) yielded the best electrical performance (0.097/0.087 Ω cm), modest strengths (16.1/3.6 MPa), and a decomposition temperature of 402°C. These results highlight how tuning filler size and composition enhances the multifunctional performance of PVDF‐based CPCs.

In this study, double percolated network of carbon nanoparticles and ceramics powder is used to uncouple electrical and thermal conductivity of polymer composite. The influence of ceramic powders on morphological properties of a biphasic conductive polymer composite (CPC) is investigated by means of rheological measurements. The biphasic materials studied are blends of a thermally conductive polymer phase (syndiotactic poly(styrene) (sPS) filled with boron nitride (BN)) with an electrically conductive polymer phase (high-density poly(ethylene) (hdPE) filled with nano-structured carbon black (NCB)) into a cocontinuous structure. The elastic modulus (with viscous modulus) was found to be the most sensitive rheological property to accurately detect the co-continuous morphology in our system. It was found to be at 40% v/v of hdPE-NCB, which can be interpreted as the phase inversion.

Waste flame-retardant polyurethane foam/ground tire rubber/carbon nanotubes composites with hierarchical segregated structures for high efficiency electromagnetic interference shielding

Multifunctional polymer foams with carbon nanoparticles

Conductive Polymer Composites (CPCs) have recently gained an extensive scientific interest as feedstock materials in Fused Filament Fabrication (FFF) Three-dimensional (3D) printing. Polylactic Acid (PLA), widely used in FFF 3D printing, as well as its Carbon Black (CB) nanocomposites at different weight percentage (wt.%) filler loadings (0.5, 1.0, 2.5 and 5.0 wt.%), were prepared via a melt mixing filament extrusion process in this study and utilized to manufacture FFF 3D printed specimens. The nanocomposites were examined for their electrical conductivity. The highest loaded 3D printed CPC (5.0 wt.%) was tested as an electrothermal Joule heating device. Static tensile, flexural, Charpy’s impact and Vickers microhardness mechanical properties were investigated for the neat and PLA/CB 3D printed nanocomposites. Dynamic Mechanical Analysis (DMA) revealed a stiffening mechanism for the PLA/CB nanocomposites. Scanning Electron Microscopy (SEM) elucidated the samples’ internal and external microstructural characteristics. The PLA/CB 5.0 wt.% nanocomposite demonstrated also antibacterial properties, when examined with a screening process, against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). It can be envisaged that the 3D printed PLA/CB CPCs exhibited a multi-functional performance, and could open new avenues towards low-cost personalized biomedical objects with complex geometry, amongst others, i.e., surgery tools, splints, wearables, etc.

Conductive polymer composites showing large positive temperature coefficient (PTC) are made of semi-crystalline polymer as an insulator and a conducting filler, whose concentration is close to the critical volume fraction. In this study, the resistivity and PTC behaviour of polyethylene filled with different carbon blacks were studied. Among the composites filled with different carbon blacks, N660 carbon black filled PE showed the greatest PTC behaviour. Large particle size, small surface area and small amount of the aggregate structure lead to large amplitude PTC behaviour (defined as the ratio of maximum resistivity to the resistivity at room temperature). The large PTC behaviour is due to some microscopic mechanism under the macroscopic thermal expansion of the polymer matrix during the melting of polymer crystal.